The present invention is directed to a method for monitoring at least one bit rate of at least one virtual connection whose connection cells incoming on a transmission link are checked with respect to their chronological frequency.
In, for example, a broad band transmission network for which, for example, an asynchronous transfer mode (ATM) is provided, the information to be transmitted can be transmitted in connection cells having a fixed length. As a performance feature of such a ATM network, virtual connections having call-associated bit rates should be capable of being established. A subscriber in this network has the possibility of selecting a suitable bit rate for his use, for example on the basis of a defined service category. Various characteristics can be provided for service categories in the ATM network, for example a medium bit rate, a peak bit rate, a burst length. The medium bit rate is the data rate averaged over a duration of the connection. The peak bit rate is the data rate averaged over a short time interval. A burst of the data rate of a connection occurs when the medium bit rate is briefly exceeded by rate that is a multiple of the medium bit rate. Frequently occurring bursts and, more importantly, long bursts can lead to problems in the switching nodes, for example buffer overflows. A limitation of burst lengths should therefore be provided. Bursts predominantly occur for connections involving data processing and the applications thereof, and often exceed ten times a medium bit rate.
By contrast thereto, normal telephone traffic generates a continuous, i.e. burst-free, data stream that continuously exhibits its maximum bit rate of, for example, 64 k bits/sec, predominantly while a person is speaking. The characteristics of service categories, for example a calculation of a call fee, should take the possible applications into consideration.
Data streams from connection cells of many subscribers are concentrated on common transmission lines in a transmission network. A misbehavior of a subscriber due to bursts in one of these connections can thus also negatively influence other connections. In order to avoid this, the bit rate reported by the subscriber should already be monitored in a connection-associated fashion when accessing the network, i.e., for example, before what is the first switching matrix network for this connection. This should occur with a monitoring according to what is referred to as a policing function.
Many virtual connections having different bit rates should be capable of being simultaneously active on a central office line. Each of the virtual connections on the central office line is assigned a number for identification, referred to as a virtual channel identifier (VCI). Several hundred VCIs must be often individually monitored given a connection of a private branch exchange or of a local network, referred to as local area network (LAN). A policing function having such performance demands has not been realized in the prior art.
A known method for monitoring individual, virtual connections works according to what is referred to as the "leaky bucket" principle. This principle, for example, is described in the Conference Report of iss Is 88, Boston, 1988, Chapter 12.2, (IEEE), in the article "The Policing Function to Control User Access in ATM Networks, Definition and Implementation" by W. Kowalk and R. Lehnert. This enables the monitoring of an established bit rate and of an established burst length. A counter, a threshold, a decrementation value as well as a decrementation clock are provided in connection associated fashion for each of the connections to be monitored. A counter value of the connection associated counter is decremented by the connection-associated decrementing value at periodic time intervals corresponding to the length of the connection-associated decrementation clock. This counter value is set to zero when negative values are reached. This connection-associated counter value is incremented each time a connection cell arrives for the monitored connection associated with this counter value. As soon as this counter value exceeds the connection-associated threshold, special handling for this connection is implemented. The virtual connection can be aborted in this special handling. Instead, a suppression of one or more connection cells can also occur, so that thereafter the connection, as in the case of a brief interruption, can again continue to exist after this reduction of its bit rate. Further, this connection can also continue to exist interruption-free in this special handling. The monitoring of the connection is modified by selecting the connection-associated parameters. The selected, medium bit rate is thus particularly monitored by the decrementation value and the decrementation clock. The maximum burst length is limited by the threshold. These parameters can be different for each of the connections. A respective connection-associated counter is required for each VCI and the connection-associated parameters should be stored connection-associated. For an identical clock for all connections, the decrementation clock can also be globally stored. Since all connection-associated counters must be processed within the respective decrementation clock, only a small number of monitorable connections is possible. As an inadequate method, a plurality of connections can be monitored in common in that their bit rates are monitored as an aggregate. For an upper transgression of the summed-up thresholds, however, a distinction as to which of the subscribers has exceeded his threshold cannot be made.